The present invention relates to foamed treatment fluids and, more particularly, to methods in which temperature is used to control the foaming and/or defoaming of foamed treatment fluids comprising an aqueous liquid, an ionic foaming surfactant, and a gas.
Foamed treatment fluids may be used in a variety of subterranean treatments, such as drilling operations, well bore cleanup operations, fracturing treatments, sand control treatments, and the like. As used herein, a “treatment fluid” refers to any fluid used in subterranean treatments for a desired function and/or a desired purpose and does not imply any particular action by the fluid. Foamed treatment fluids generally include an aqueous liquid, a surfactant for foaming and/or stabilizing the fluid, and a gas. In addition to being lightweight, foamed treatment fluids may effectively carry particulates (e.g., drill cuttings, particulate debris, proppant particulates). Additionally, foamed treatment fluids have low fluid loss properties, reducing or removing the need for fluid loss control additives.
Drilling operations are one example of a subterranean treatment that may use a foamed treatment fluid. During drilling operations, a foamed treatment fluid (e.g., a foamed drilling fluid) passes down through the inside of the drill string, exits through the drill bit, and returns to the drilling rig through the annulus between the drill string and well bore. The circulating foamed drilling fluid, among other things, lubricates the drill bit, transports drill cuttings to the surface, and balances the formation pressure exerted on the well bore. Among other things, the foamed drilling fluid should have sufficient foam quality to suspend drill cuttings. Foamed treatment fluids also may be used in a variety of well bore cleanup operations to transport and remove debris particulates (e.g., drill cuttings, formation debris, etc.) from the well bore or the near well bore region.
Another example of a subterranean treatment that may use a foamed treatment fluid is a fracturing treatment. In a fracturing treatment, a foamed treatment fluid (e.g., a foamed fracturing fluid) is introduced into a well bore at or above a pressure sufficient to create or enhance one or more fractures in a portion of the subterranean formation. The foamed fracturing fluid may comprise particulates, often referred to as “proppant particulates,” that are deposited in the fractures. The proppant particulates function to prevent the fractures from fully closing upon the release of pressure, forming conductive channels through which fluids may flow to the well bore. After the fracturing operation is complete, the pressure on the well bore is released. This allows the gas in the foamed fracturing fluid to expand and, with this expansion, the energized foamed fracturing fluid flows from the formation, flows into the well bore, and exits the well bore at the surface.
Foamed treatments fluids also may be used in sand control treatments, such as gravel packing. In gravel pack treatments, the foamed treatment fluid suspends gravel particulates for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation zones, to form a gravel pack that enhances sand control. One common type of gravel packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size designed to prevent the passage of formation sand. The gravel particulates act, inter alia, to prevent the formation particulates from occluding the screen or migrating with the produced hydrocarbons, and the screen acts, inter alia, to prevent the gravel particulates from entering the production tubing. Once the gravel pack is substantially in place, the pressure on the well bore is released. This allows the gas in the foamed treatment fluid to expand and, with this expansion, the foamed treatment fluid flows from the formation, into the well bore, and exits the well bore at the surface.
Defoaming of the foamed treatment fluid subsequent to use may be desirable for a number of reasons. For instance, defoaming may allow the treatment fluid and its components to be recycled for subsequent use. Further, defoaming prior to mechanical separation of the particulates from the foamed treatment fluid should reduce the expense and complexity associated with the separation process. In some instances, after recovery from the well bore, the foamed treatment may be placed in a settling pond where, over time, the foam will dissipate. But storage of the foamed treatment fluid to allow sufficient time for dissipation of the foam may be problematic, due to, among other things, long turnaround times and increased environmental impact. Thus, in certain circumstances it may be desirable to control the defoaming process.
Controlling the pH of the foamed treatment fluid is one method that has been used to facilitate foaming and defoaming. In some instances, certain surfactants and combinations thereof have been used to facilitate foaming and defoaming in response to pH changes. For example, after the foamed treatment fluid has been recovered from the well bore, it may be defoamed by lowering its pH. However, controlling the pH of the foamed treatment fluid may increase the complexity of the subterranean treatment due to, among other things, the use of buffers for providing the needed pH for foaming and also the use of acids for lowering the pH of the foamed treatment fluid sufficiently for defoaming.